1. Field of the Invention
The present invention relates to an improvement in a photoelectric switching apparatus.
The present invention particularly concerns a photoelectric switching apparatus usable in various kind of usages.
2. Prior Arts
Photoelectric switching apparatuses have been recently widely used for operation of an automatic door or the like system. In such conventional photoelectric switching apparatuses, modulated lights are used in order to avoid maloperation due to light noise. And in a receiver part of the apparatus the modulated light is detected by utilizing a synchronizing signal obtained from the light transmitter of the system. By use of such synchronized detection, the true signal to be detected is selectively taken out by removing the noises therefrom. In such system, in case the light transmitter part and the light receiver part are disposed considerably apart and both units are operated by different power lines, it is difficult to convey the synchronizing signal from the light transmitter part to the light receiver part. In such apartly disposed system, in place of using such synchronizing signal, such systems have been constituted that the pulse signals obtained by detection of the received light is integrated for a predetermined time period and an output signal is issued when the integrated signal reaches a predetermined level. However, such system has shortcomings that its response is relatively slow due to the use of the integration circuit, and that the integration circuit can not dicriminate the genuine signal when a number of the noise pulses are input sequentially.
An improvement for overcoming the shortcomings of the conventional system has been proposed as shown in FIG. 1, wherein a light transmitter part A comprises an oscillator 8, a light transmitter circuit 1 and a light transmitting transducer 101, and a light receiver part B comprises a light receiving transducer 201, a light receiver circuit 2, an amplifier 9, a waveform shaper 10, a square wave generator 3 an integration circuit 4 and comparator 11, and the output of the waveform shaping circuit 11 is given to an output circuit 5. The provision of the square wave generator 3 serves to produce a square wave with a considerable pulse width at each triggering by an input pulse signal of narrow pulse width, thereby enabling shortening the time period required for the integration circuit to produce its output by integrating the input pulse signal thereto. However, such conventional systems still have the drawback that input of the sequential noises are likely to cause maloperation of the circuit. Therefore, it is still required to operate the receiving part by utilizing a synchronizing signal.
Furthermore, hitherto there are three different types of such photoelectric switches. The first kind is one where, as shown in FIG. 2(a), the light transmitter part A and the light receiver part B are separately disposed opposing each other with a path of detecting object M inbetween. In this case, the light is intercepted by the detecting object M. This type is hereinafter called a "separate-disposition type." The second way is one where, as shown in FIG. 2(b), the light transmitter part A and the light receiver part B are disposed in a close position and a light reflecting means D is disposed opposing to both parts with the path of detecting object M or M' inbetween so as to reflect the light to the light receiving part B. In this case too, the light is intercepted by the detecting object M. This case is hereinafter called a "combined-disposition light interception type." The third way is one where, as shown in FIG. 2(c), the light transmitter part A and the light receiver part B are disposed in a close position, both facing the path of the detection object M. In this case the light is reflected by the detecting object M. This case is hereinafter called a "combined-disposition light reflection type."
As is obvious from the comparison of the type of FIG. 2(a) and the types of FIG. 2(b) and FIG. 2(c), the former type has the light transmitter part A in a separate case from the receiver part B, and hence detection of the received signal is made in a non-synchronized way, while the latter two types have the light transmitter part A in the same case with the receiver part B, and hence the detection is made in a synchronized way.
Furthermore, in the types of FIG. 2(a) and FIG. 2(b), the light interception is detected to produce an output signal. In these types, in order to remove erroneous detection output at the initial transient time immediately after a switching on of the apparatus, the integration circuit 4 must be specially operated, for instance that, a special circuitry is formed for quick charging of a timer capacitor in the integration circuit 4 during this initial transient stage. On the contrary, in the type of FIG. 2(c), the light reflection is detected to produce an output signal. In this type, in order to remove erroneous detection output at the initial transient time immediately after a switching on of the apparatus, the integration circuit 4 must be oppositely operated to the above case, that is, a special circuitry is formed for quick discharging of a timer capacitor in the integration circuit 4 during this initial transient stage. Therefore, hitherto, though having almost the same circuit configurations as each other, the apparatuses of the types of FIG. 2(a), FIG. 2(b) and FIG. 2(c) have been separately manufactured with respect to the abovementioned different special circuitries in the integration circuit 4, as well as, the above-mentioned inclusion of the transmitter part and the synchronized detection.